Stationary position detection circuit and motor drive circuit

ABSTRACT

A stationary position detection circuit and a motor drive circuit capable of more properly detecting the rotor position are disclosed. The stationary position detection circuit supplies an alternating current to each phase load of the motor. The time during which the current flows in a first direction and the time during which the current flows in a second direction opposite to the first direction are converted into electrical signals and amplified. In accordance with the value of the electrical signals, the position of the motor rotor in stationary mode is determined. The use of the alternating current, unlike the kickback voltage, makes it possible to improve the detection accuracy by amplifying the electrical signals with an increased number of alternations. An increased number of alternations can amplify the electrical signals without increasing the value of the alternating current, and therefore, unlike in the case of the kickback voltage, the alternating current of a large value is not required. As a result, the alternating current can be reduced to a small value and the vibration can be suppressed.

This application is a continuation of U.S. patent application Ser. No.11/476,052 filed Jun. 28, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a stationary position detection circuitand a Hall sensorless motor drive circuit capable of detecting theposition of a motor rotor.

2. Description of the Background Art

In driving a motor having a rotor such as a small three-phase DCbrushless motor, the motor drive circuit is required to be kicked at thetime of starting. In the process, unless the rotor position can bedetected properly, the proper starting is impossible.

The rotor position can be detected by arranging a Hall sensor configuredof a Hall element in the neighborhood of the motor rotor. The use of theHall sensor, however, leads to an increased cost and a bulkiness.Currently, therefore, vigorous efforts are made to develop what iscalled a Hall sensorless motor using no Hall sensor.

In the Hall sensorless motor, no induction voltage (counterelectromotive voltage) is generated as long as the motor is stationary,so that the position of the rotor cannot be detected. As described inJapanese Patent Application Laid-Open Nos. 2002-345286, 2002-335691 and2002-315385, therefore, a method has been developed in which the lengthof the kickback time for turn-off operation is detected by a stationaryposition detection circuit thereby to detect the position of the rotorof a motor in stationary mode.

Japanese Patent Application Laid-Open No. 2003-47280 is also availableas another patent document related to the present patent application.

In the case where the kickback voltage at the time of turning off ismeasured as in the stationary position detection circuit described inJapanese Patent Application Laid-Open Nos. 2002-345286, 2002-335691 and2002-315385, the difference in the kickback voltage value with aminuscule inductance difference depending on the rotor position whilethe motor is stationary makes it possible to detect the rotor positionof a stationary motor by detecting the length of the kickback time.

In the detection method using the kickback voltage, however, a largekickback voltage is required to be generated by supplying a largekickback current (for example, about 1 A) to detect the minusculeinductance difference due to the difference of rotor position. This isby reason of the fact that a large kickback voltage is required tosufficiently recognize the difference in the length of the kickbacktime. The large kickback current is a cause of vibrations.

Also, in the detection method using the kickback voltage, theinformation indicating the inductance difference can be obtained onlyfor the very short period during which the kickback occurs, andtherefore the information may not be sufficiently detected.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a stationary positiondetection circuit and a motor drive circuit capable of detecting therotor position more properly.

According to a first aspect of the present invention, a stationaryposition detection circuit for a motor including a rotor and at leastone-phase load detects the position of the rotor in stationary mode, andincludes a current amount detector, a time counter, a time differenceamplifier and a position determinator.

The current amount detector operates in such a manner that analternating current flowing alternately in a first direction and asecond direction opposite to the first direction is rendered to flowthrough the load by a control circuit for controlling an invertercircuit for driving the motor, the fact that the alternating currentflowing in the first direction has reached a value a is detected, afterwhich the alternating current is rendered to flow in the seconddirection by gradually decreasing amount of the alternating currentthrough the control circuit, and the fact that the alternating currentflowing in the second direction has reached a value β equal to andopposite in sign to the value α is detected, after which the alternatingcurrent is rendered to flow in the first direction again by graduallydecreasing amount of the alternative current through the controlcircuit, the detection of the values α and β and the control of thealternating current by the control circuit being subsequently repeated apredetermined number of times.

The time counter counts the first time for which the alternating currentchanges from α to β and the second time for which the alternatingcurrent changes from β to α.

The time difference amplifier converts the counted first time and secondtime into electrical signals and amplifies the electrical signals inaccordance with the accumulation of the first time and second time bythe predetermined number of times, and

The position determinator determines the position of the rotor instationary mode in accordance with the value of the electrical signals.

The time counter counts the first and second time, the time differenceamplifier converts the first and second time to electrical signals andamplifies the electrical signals in accordance with a predeterminednumber of accumulations of the first and second time. The use of thealternating current, unlike the kickback voltage, makes it possible toamplify the electrical signals with an increased number of alternationsfor a higher detection accuracy. Also, in view of the fact that anincreased number of alternations makes it possible to amplify theelectrical signals without increasing the alternating current values αand β, the alternating current of a large value is not required unlikethe kickback voltage. As a result, the alternating current can bereduced to a small value (about 0.1 A, for example) and the vibrationscan be suppressed. Thus, a stationary position detection circuit capableof detecting the rotor position more properly is realized.

According to a second aspect of the present invention, a motor drivecircuit includes the stationary position detection circuit according tothe first aspect, the inverter and the control circuit.

In view of the fact that the motor drive circuit includes the stationaryposition detection circuit according to the first aspect, a motor drivecircuit capable of detecting the rotor position more properly isrealized.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a motor drive circuit and a motor accordingto a first embodiment;

FIG. 2 is a diagram showing the principle of the present invention;

FIG. 3 is a diagram showing a detailed configuration of the stationaryposition detection circuit according to the first embodiment;

FIG. 4 is a diagram showing a detailed configuration of the currentamount detector in the stationary position detection circuit;

FIG. 5 is a diagram showing a detailed configuration of the timecounter, the time difference amplifier and the rotor positiondeterminator in the stationary position detection circuit;

FIG. 6 is a timing chart while the stationary position detection circuitdetects the stationary rotor position before kicking at the time ofstarting;

FIG. 7 is a partly enlarged timing chart for an alternating currentgeneration period between U and V phases;

FIG. 8 is a circuit diagram for considering the transient phenomenonduring the period TA with a DC voltage applied to a load having aresistance and an inductance;

FIG. 9 is a circuit diagram for considering the transient phenomenonduring the period TB;

FIG. 10 is a diagram showing the operation of the inverter circuit;

FIG. 11 is a diagram showing the operation of the inverter circuit;

FIG. 12 is a diagram showing the operation of the inverter circuit;

FIG. 13 is a diagram showing the operation of the inverter circuit;

FIG. 14 is a diagram for explaining the relation of correspondencebetween the result of generating the alternating current between thephases and determining the rotor position on the one hand and the rotorposition on the other hand;

FIG. 15 is a diagram for explaining the relation of correspondencebetween the result of generating the alternating current between thephases and determining the rotor position on the one hand and the rotorposition on the other hand;

FIG. 16 is a diagram showing the stationary position detection circuitaccording to a second embodiment; and

FIG. 17 is a diagram showing the stationary position detection circuitaccording to a third embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

According to the first embodiment, there are provided a stationaryposition detection circuit and a motor drive circuit in which analternating current is supplied to a motor load and the time duringwhich the current flows in a first direction and the time during whichthe current flows in a second direction opposite to the first directionare converted into electrical signals, which are amplified to determinethe position of the motor rotor in stationary mode according to thevalue of the electrical signals.

FIG. 1 is a diagram showing a motor drive circuit and a motor accordingto this embodiment. As shown in FIG. 1, the motor 1 is, for example, athree-phase DC brushless Hall sensorless motor including a rotor 10 of apermanent magnet and a stator 11 configured of a three-phase load withan armature coil wound on a field core. The load of the stator 11 existsfor each of the phases U, V, W and coupled to each other at a center tap(CT).

The motor drive circuit, on the other hand, includes an inverter circuit2 for driving the motor 1 with an output signal 2 a thereof, an outputtransistor control circuit 3 for controlling the inverter circuit 2 witha signal 3 a thereof, a stationary position detection circuit 4 fordetecting the position of the rotor 10 in stationary mode, a positiondetection comparator 5 for detecting the position of the rotor 10 inoperation, a position detection mask circuit 6 for masking a part of theoutput signal 5 a of the position detection comparator 5, a sensorlessdrive operation circuit 7 for performing the arithmetic operation fordriving in response to the output signal 6 a of the position detectionmask circuit 6, and a signal select circuit 8 for supplying the outputtransistor control circuit 3 with, as an output signal 8 a, either theoutput signal 7 a of the sensorless drive operation circuit 7 or theoutput signal 4 a of the stationary position detection circuit 4. Thestationary position detection circuit 4 works while the motor isstationary, and the sensorless drive operation circuit 7 functions whilethe motor is rotating. The signal 4 b between the two circuits is ashake-hand signal for the operation of the two circuits.

The inverter circuit 2 is a three-phase inverter circuit havingtransistors Q1 to Q6, in which the transistors Q1, Q2 connected inseries make up a first arm, the transistors Q3, Q4 connected in seriesmake up a second arm, and the transistors Q5, Q6 connected in seriesmake up a third arm. The junction between the transistors Q1, Q2 isconnected to the U-phase load, the junction between the transistors Q3,Q4 is connected to the V-phase load, and the junction between thetransistors Q5, Q6 is connected to the W-phase load. An end of each armis applied with a power supply voltage VCC, and the other end of eacharm supplied with a grounding voltage GND through a resistor 21 fordetecting the current amount.

FIG. 2 is a diagram showing the principle of the present invention. Inthis example, an alternating current is supplied between the U-phaseload and the V-phase load of the stator 11. The direction from theU-phase load to the V-phase load is defmed as a positive direction andthe other direction as a negative direction. Also, the U-phase load andthe V-phase load are collectively defined as a load 11 a, and the effectthat the magnetic lines of force from the rotor 10 have on the load 11 ais indicated by a magnet 10 a as a simulation.

Currents flow in both positive and negative directions in the load 11 awhile the motor is rotating. The value of the resistor R of the load 11a remains constant regardless of the physical position of the rotor 10and the direction of the current flowing in the load 11 a. The value ofthe inductance L of the load 11 a, however, varies with the physicalposition of the rotor 10 and the direction of the current flowing in theload 11 a. This is by reason of the fact that the strength of themagnetic lines of force of the magnet 10 a and the strength of themagnetic lines of force generated by the current flowing in the load 11a affect the value of the inductance L of the load 11 a.

The value of the inductance L of the load 11 a changes with the physicalposition of the rotor 10 in stationary mode and the direction of thecurrent flowing in the load 11 a not only while the motor is rotatingbut also while the rotor 10 is stationary. The magnitude of the value ofthe inductance L of the load 11 a corresponds to the physical positionof the rotor 10 and the direction of the current flowing in the load 11a.

Specifically, by defining the aforementioned relation of correspondencein advance, the physical position of the rotor 10 can be determined bydetecting the value of the inductance L of the load 11 a. This isdescribed in detail later with reference to FIGS. 14, 15. According tothe present invention, the position of the rotor 10 in stationary modeis detected by the stationary position detection circuit 4 before kickat the time of starting.

FIG. 3 is a diagram showing a detail configuration of the stationaryposition detection circuit 4 according to this embodiment. As shown inFIG. 3, the stationary position detection circuit 4 includes a currentamount detector 40, a time counter 41, a time difference amplifier 42and a rotor position determinator 43.

The current amount detector 40 receives a signal 2 b of the voltagegenerated by a resistor 21 in the inverter circuit 2, and based on thissignal, generates a detection signal 40 a. Based on the detection signal40 a, the time counter 41 counts the time during which the alternatingcurrent flows in the first direction under each phase load of the stator11 and the time during which the alternating current flows under eachphase load of the stator 11 in the second direction opposite to thefirst direction, and outputs a signal S4 as a current signal.

Also, the time difference amplifier 42 converts the signal S4constituting a current signal into a voltage signal S3, and outputs byamplifying the voltage signal S3 corresponding to the accumulation, bythe number of alternations of the alternating current, of the timeduring which the alternating current flows in the first and seconddirection under each phase load of the stator 11. The rotor positiondeterminator 43 determines the position of the rotor in stationary modein accordance with the value of the voltage signal S3.

FIG. 4 is a diagram showing a detailed configuration of the currentamount detector 40. The current amount detector 40 includes a powersupply 400, a comparator 401, an AND gate circuit 402, a D-flip-flop 403and a mask signal generating circuit 404. In the comparator 401, thevoltage drop Vr across the resistor 21 generated by the alternatingcurrent in the inverter circuit 2 is compared with a predeterminedvoltage V1 generated by the power supply 400, and in the case where thevoltage drop Vr is larger than the voltage V1, the output of thecomparator 401 is activated.

The AND gate circuit 402 calculates the logic product of the mask signal6 b output from the mask signal generating circuit 404 and the output ofthe comparator 401, and outputs a signal Sr. The D-flip-flop 403 outputsthe output Q as a detection signal 40 a. Also, the inverted output/Q isan inverted signal of the output Q and applied to the input D of theD-flip-flop 403. The signal Sr is applied to the clock input T of theD-flip-flop 403. The mask signal generating circuit 404 generates a masksignal 6 b.

FIG. 5 is a diagram showing a detailed configuration of the time counter41, the time difference amplifier 42 and the rotor position determinator43 in the stationary position detection circuit 4. The time counter 41includes a current source 410, a first switch 411 for selectivelyoutputting a current I1 from the current source 410 when the logic valueof the detection signal 40 a is Low, and a second switch 412 forselectively outputting the current I1 from the current source 410 whenthe logic value of the detection signal 40 a is Hi. The output from thefirst switch 411 is a signal S4 a constituting one part of the signalS4, and the output from the second switch 412 is a signal S4 bconstituting the other part of the signal S4.

The time difference amplifier 42 includes a first capacitor 423 of apredetermined capacitance charged by the output of the first switch 411and a second capacitor 421 having the same capacitance as the firstcapacitor 423 and charged by the output of the second switch 412. Oneend of the first capacitor 423 is connected to the first switch 411, andthe other end thereof is supplied with the grounding potential GND. Oneend of the second capacitor 421 is connected to the second switch 412,and the other end thereof applied with the grounding potential GND. Thepotential at one end of the first capacitor 423 constitutes a signal S3a making up one part of the voltage signal S3, and the potential at oneend of the second capacitor 421 constitutes a signal S3 b making up theother part of the voltage signal S3.

Also, the time difference amplifier 42 includes a transistor 422 todischarge the first capacitor 423 by applying the grounding potentialGND to one end of the first capacitor 423 during the activation of areset signal S2 and a transistor 420 to discharge the second capacitor421 by applying the grounding potential GND to one end of the secondcapacitor 421 during the activation of the reset signal S2.

The rotor position determinator 43 includes a comparator 430 having thepositive and negative terminals thereof supplied with the signal S3 bmaking the other part of the voltage signal S3 and the signal S3 amaking up the one part of the voltage signal S3, respectively, so thatthe output logic value functions as a determination signal 4 a for theposition of the rotor in stationary mode.

Next, the operation of the stationary position detection circuit 4according to this embodiment is explained. FIG. 6 is a timing chart forthe stationary position detection circuit 4 to detect the position ofthe rotor 10 in stationary mode before kick at the time of starting.

As shown in FIG. 6, according to the present invention, the alternatingcurrent is supplied between U and V phases, between V and W phases andbetween W and U phases before determining the kick position.Specifically, during the period Tul, the alternating current is suppliedbetween U and V phases to detect the position of the rotor 10, andduring the subsequent period Tu2, the information on the detectionresult between U and V phases is stored in the output transistor controlcircuit 3. Incidentally, the U-phase current and the V-phase currenthave complementary waveforms due to the fact that the current applied tothe U-phase load (or the V-phase load) is set as positive, and thecurrent flowing out of the U-phase load (or the V-phase load) asnegative.

In a similar fashion, the alternating current is supplied between V andW phases during the period Tv1, and during the subsequent period Tv2,the information on the detection result between V and W phases is storedin the output transistor control circuit 3. Also, the alternatingcurrent is supplied between W and U phases during the period Tw1, andthe information on the detection result between W and U phases is storedin the output transistor control circuit 3 during the subsequent periodTw2.

FIG. 7 is an enlarged timing chart for one part U1 of the alternatingcurrent generation period between U and V phases in FIG. 6. In the motordrive circuit according to the present invention, the time of transientresponse of the current flowing in each phase load of the stator 11,which is affected by the magnetic field of the rotor 10, is countedthereby to determine the magnitude of the inductance value, and based onthe result thereof, the physical position of the rotor 10 is determined.

First, as indicated by the period TA in FIG. 7, the stationary positiondetection circuit 4, through the output transistor control circuit 3 forcontrolling the inverter circuit 2, generates a current flowing in thefirst direction from U to V phase, which current is increased to a valueα (for example, an absolute value 0.1 A). Once the current flowing inthe first direction from U to V phase has reached the value α, thestationary position detection circuit 4 reduces and returns the currentvalue back to 0 A through the output transistor control circuit 3 asshown by the period TB in FIG. 7. Then, a current flowing from V to Uphase in the second direction opposite to the first direction isgenerated, and increased to reach a value β of opposite sign to thevalue α (i.e., the absolute value 0.1 A like the value α, for example).

Once the current flowing in the second direction from V to U phase hasreached the value β, the stationary position detection circuit 4 reducesthe current value back to 0 A through the output transistor controlcircuit 3 as shown by the period TC in FIG. 7. Then, a current flowingin the first direction from U to V phase is generated again, andincreased to reach the value α. Subsequently, the stationary positiondetection circuit 4, through the output transistor control circuit 3,generates the current alternating between values α and β by the numberof times equal to the number of alternations of the alternating current.

A circuit equation is formulated with the load 11 a of FIG. 2 as a modelfor each of the periods TA to TC. First, FIG. 8 is a circuit diagram forconsidering the transient phenomenon during the period TA with a DCvoltage E applied to the load 11 a having the resistance R and theinductance L. In the circuit diagram of FIG. 8, the initial value of thecurrent flowing in the load 11 a is set to io.

In this circuit diagram, the current i(t) changing with time t is givenas follows. $\begin{matrix}{{i(t)} = {{\frac{E}{R}\left\{ {1 - {\mathbb{e}}^{{- \frac{R}{L}}t}} \right\}} + {i_{0}{\mathbb{e}}^{{- \frac{R}{L}}t}}}} & (1)\end{matrix}$

As shown in FIG. 7, no current flows in the beginning of the period TA,and therefore the second term of Equation 1 is considered 0. In otherwords, the current i(t) during the period TA is expressed as follows.$\begin{matrix}{{i(t)} = {\frac{E}{R}\left\{ {1 - {\mathbb{e}}^{{- \frac{R}{L}}t}} \right\}}} & (2)\end{matrix}$

Equation 2 is modified as follows. $\begin{matrix}{t = {{{- \frac{L}{R}} \cdot \ln}\left\{ {1 - \frac{\alpha}{\frac{E}{R}}} \right\}}} & (3)\end{matrix}$

This equation represents time t.

Next, consider the transient phenomenon during the period TB. FIG. 9 isa circuit diagram for this purpose. In the beginning of the period TB, acurrent of initial value α flows and therefore, in FIG. 9, the current αis indicated in the same direction as io of FIG. 8. At the end of theperiod TB, on the other hand, a current of value β inverted in sign fromthe value α flows, and therefore, in FIG. 9, the current β opposite indirection to the current α is also indicated. Also, a voltage oppositein direction to the voltage for the period TA is applied to the load 11a under the control of the inverter 2, and therefore, the direction ofthe DC voltage E in FIG. 9 is opposite to the direction of the DCvoltage E of FIG. 8.

In this circuit diagram, an equation for the time point when the currentof value β flows is considered on the basis of Equation 1 as follows.$\begin{matrix}{\beta = {{\frac{E}{R}\left\{ {1 - {\mathbb{e}}^{{- \frac{R}{L}}t}} \right\}} - {\alpha\mathbb{e}}^{{- \frac{R}{L}}t}}} & (4)\end{matrix}$

Equation 4 is modified as follows. $\begin{matrix}{{\mathbb{e}}^{{- \frac{R}{L}}t} = \frac{\frac{E}{R} - \beta}{\frac{E}{R} + \alpha}} & (5)\end{matrix}$

Equation 5 can be further modified as follows. $\begin{matrix}{t = {{- \frac{L}{R}} \cdot {\ln\left\lbrack \frac{\frac{E}{R} - \beta}{\frac{E}{R} + \alpha} \right\rbrack}}} & (6)\end{matrix}$

This equation represents time t. In FIG. 7, the period TB is expressedas time t1 of the detection signal 40 a, and therefore, t1 is employedin place of time t. Also, assuming that the inductance L of the load 11a for the period TB is L1, Equation 6 can be expressed as follows.$\begin{matrix}{{t\quad 1} = {{- \frac{L\quad 1}{R}} \cdot {\ln\left\lbrack \frac{\frac{E}{R} - \beta}{\frac{E}{R} + \alpha} \right\rbrack}}} & (7)\end{matrix}$

Next, consider the transient phenomenon for the period TC. In this case,as understood from FIG. 7, the only difference is that the initial valueis β and the end value is α, and the other points are similar to thosefor the period TB. In FIG. 9 and Equation 6, therefore, the values α andβ for the period TB are replaced with each other. Thus, the circuitequation for the period TC is given as follows. $\begin{matrix}{t = {{- \frac{L}{R}} \cdot {\ln\left\lbrack \frac{\frac{E}{R} - \alpha}{\frac{E}{R} + \beta} \right\rbrack}}} & (8)\end{matrix}$

In FIG. 7, the period TC is expressed by time t2 of the detection signal40 a. By employing t2 in place of time t and setting the inductance ofthe load 11 a for the period TC to L2, therefore, Equation 8 can beexpressed as follows. $\begin{matrix}{{t\quad 2} = {{- \frac{L\quad 2}{R}} \cdot {\ln\left\lbrack \frac{\frac{E}{R} - \alpha}{\frac{E}{R} + \beta} \right\rbrack}}} & (9)\end{matrix}$

Comparison between Equations 7 and 9 shows that as long as α and β areequal to each other in absolute value, the ratio between time t1 andtime t2 is expressed as follows.t1:t2=L1:L2  (10)

As understood from Equation 10, the ratio between the inductances L1 andL2 coincides with the ratio between the time t1 for which thealternating current changes from α to β in value and the time t2 forwhich the alternating current changes from β to α in value. By countingthe times t1 and t2 and specifying the relative magnitudes thereof,therefore, the relation between the U-V load 11 and the position of therotor 10 can be defined.

Incidentally, FIGS. 10 to 13 are diagrams showing the operation of theinverter circuit 2 for the periods TA to TC. FIG. 10 shows a case inwhich the alternating current flows increasingly in the first directionfrom U phase to V phase (the portion of the periods TA and TC in FIG. 7during which the current value is larger than 0 A). In this case, thetransistors Q1, Q4 in the inverter circuit 2 turn on, while the othertransistors remain off.

FIG. 11 shows a case in which the alternating current flowing in thefirst direction is attenuated (the portion of the period TB in FIG. 7during which the current value is larger than 0 A). In this case, thetransistors Q2, Q3 in the inverter circuit 2 turn on, while the othertransistors remain off. FIG. 12 shows a case in which the alternatingcurrent flows increasingly in the second direction from V phase to Uphase (the portion of the period TB in FIG. 7 during which the currentvalue is smaller than 0 A). In this case, the transistors Q2, Q3 in theinverter circuit 2 turn on, while the other transistors remain off. FIG.13 shows a case in which the alternating current flowing in the seconddirection is attenuated (the portion of the period TC in FIG. 7 duringwhich the current value is smaller than 0 A). In this case, thetransistors Q1, Q4 in the inverter circuit 2 turn on, while the othertransistors remain off.

The operation of each circuit for generating the alternating current anddetermining the position of the rotor 10 is explained. First, the valueof the voltage V1 generated by the power supply 400 in the currentamount detector 40 shown in FIG. 4 is set to a value slightly lower thanthe maximum value of the voltage drop Vr across the resistor 21 in theinverter circuit 2 for each period of TB, TC, etc.

The value of the voltage drop Vr across the resistor 21 is the productof the current α and the resistance value of the resistor 21 in thebeginning of the period TB. With the lapse of the period TB, the currentvalue decreases, and therefore the value of the voltage drop Vr alsodecreases along a waveform similar to that of the current value.

During the decrease in the current value, a spike SP1 appears in thevoltage drop Vr. A current in the direction opposite to the directionfrom the power supply Vcc toward the grounding potential GND is flowingin the transistors Q2, Q3 (dashed arrow in FIG. 11), and a voltage of aninverse bias is applied between drain and source thereof. At about apoint where the current changes from the first to the second direction(at about a point where FIG. 11 changes to FIG. 12), therefore, thecharge accumulated in the drain-source capacitance flows sharply throughthe resistor 21 in addition to the current in the direction from thepower supply Vcc toward the grounding potential GND (solid arrow in FIG.12). It is for this reason that the voltage drop Vr develops the spikeSP1.

The mask signal 6 b is for masking the spike SP1 not to be detected, andoutput from the mask signal generating circuit 404 for a predeterminedlength of time (say, 2 μsec) from the time point when the currentreaches the value α or β. The mask signal generating circuit 404 detectsthe signal 3 a to detect the turn on/off time of the transistors Q1 toQ6 and outputs a mask signal 6 b for a predetermined length of time fromthe time of turn on/off. The mask signal 6 b, as shown in FIG. 7, is aLow active signal. During the mask period, the mask signal 6 b is Lowand therefore an AND gate circuit 402 continues to output a Low signalregardless of the output of the comparator 401.

With the attenuation of the alternating current flowing in the firstdirection while the alternating current increasingly flows in the seconddirection, the value of the voltage drop Vr across the resistor 21approaches the value of the product of the current β and the resistancevalue of the resistor 21 in the last half of the period TB. As a result,the value of the voltage drop Vr also increases with a waveform similarto that of the current value.

Once the value of the voltage drop Vr increases beyond the value of thevoltage V1 generated by the power supply 400, the comparator 401activates the output thereof to Hi level. At this time point, the maskperiod is already ended and the mask signal 6 b assumes a Hi level.Thus, the AND gate circuit 402 outputs a signal Sr as an activatedoutput from the comparator 401. It is for this reason that the signal Sris generated in pulses in FIG. 7.

With the start of the period TC, the AND gate circuit 402 receives themask signal 6 b activated to Low again, and outputs a Low signal withoutregard to the output of the comparator 401. Upon the lapse of the maskperiod in the period TC, the AND gate circuit 402 outputs the signal Srfrom the comparator 401 activated when the value of the voltage drop Vrincreases beyond the value of the voltage V1. During the subsequentperiods, the AND gate circuit 402 similarly outputs a pulse-like signalSr. In this way, the AND gate circuit 402 functions as a logic gatecircuit for passing the. output of the comparator 401 only in each lasthalf of the time t1 and t2.

The D-flip-flop 403 has the inverted output/Q thereof applied to theinput D thereof. With the activation of the clock input T, therefore,the output Q thereof alternates between Hi and Low states. TheD-flip-flop 403, with the signal Sr applied to the clock input T,functions to invert the logic value of the output with the activation ofthe output of the AND gate circuit as a motive.

The inverted output of the D-flip-flop 403 constitutes a detectionsignal 40 a for the values α and β and a control signal 40 a for thealternating current. Specifically, by the control signal 40 a shown inFIG. 3, the current amount detector 40, through the output transistorcontrol circuit 3 for controlling the inverter circuit 2 for driving themotor 1, so operates that the alternating currents flowing alternatelyin the first direction from U to V phases and in the second directionfrom V to U phases are rendered to flow through the load 11 a between Uand V phases, and after detection that the alternating current flowingin the first direction has reached the value α, the alternating currentis reduced gradually through the output transistor control circuit 3 toflow in the second direction. Also, after detection that the alternatingcurrent flowing in the second direction has reached the value β, thealternating current is gradually reduced through the output transistorcontrol circuit 3 to flow again in the first direction. Subsequently,the detection of the values α and β and the control of the alternatingcurrent through the output transistor control circuit 3 are repeated bythe number of times equal to the number of alternations.

Incidentally, the reset signal S1 shown in FIG. 4 is activated after theflow of the alternating current between U and V phases before thealternating current next begins to flow between V and W phases. Insimilar fashion, the reset signal S1 is activated after the flow of thealternating current between V and W phases before it next begins to flowbetween W and U phases, so that the result of detection between thephases may have no effect on the next detection between the phases.

The time counter 41 shown in FIGS. 3, 5, in accordance with thedetection signal 40 a, so functions as to count the time t1 (the periodTB in FIG. 7) for which the alternating current changes from value α toβ and the time t2 (the period TC in FIG. 7) for which the alternatingcurrent changes from value β to α and output the current signal S4 (S4a, S4 b) for the time t1, t2 thus counted.

Specifically, the first switch 411 in the time counter 41, based on thedetection signal 40 a, counts the time t1 by selectively outputting thecurrent I1 from the current source 410 during the period (the Low periodof the detection signal 40 a) after detection of the value α to thedetection of the value β by the current amount detector 40. Similarly,the second switch 412 in the time counter 41, based on the detectionsignal 40 a, counts the time t2 by selectively outputting the current I1from the current source 410 during the period (the Hi period of thedetection signal 40 a) from the detection of the value β to thedetection of the value α by the current amount detector 40.

The time difference amplifier 42 shown in FIGS. 3, 5 converts the signalS4 constituting a current signal into a voltage signal S3 and amplifiesthe voltage signal S3 (S3 a, S3 b) in accordance with the accumulationof the time t1, t2 by the number of alternations. Specifically, thefirst capacitor 423 accumulates the charge each time the current signalS4 a is input from the first switch 411 turned on during the time t1,and increases the accumulated charge in accordance with the accumulationof time t1 by the number of alternations thereby to amplify the signalS3 a. In similar manner, the second capacitor 421 accumulates the chargeeach time the current signal S4 b is input from the second switch 412turned on during the time t2, and increases the accumulated charge inaccordance with the accumulation of time t2 by the number ofalternations thereby to amplify the signal S3 b.

The first capacitor 423 and the second capacitor 421 have the samecapacitance value and are supplied with the same current I1. Assumingthat time t1 and t2 are the same, therefore, the signals S3 a and S3 btake the same value. In the case where time t1 and t2 are different invalue, however, the difference between time t1 and t2 is emphasized inoutput in view of the fact that the signals S3 a, S3 b are amplified bythe number of alternations.

Incidentally, the reset signal S2 shown in FIG. 5 is activated after thealternating current flows between U and V phases before next beginningto flow between U and W phases, and similarly activated after thealternating current flows between V and W phases before next beginningto flow between W and U phases. This signal is for preventing thedetection result between the phases (the charge amount of the firstcapacitor 423 and the second capacitor 421) from affecting the nextdetection between the phases.

The comparator 430 of the rotor position determinator 43 shown in FIG. 5compares the magnitude of the signal S3 a with that of the signal S3 band outputs a Hi logic value in the case where the signal S3 b is largerthan the signal S3 a, and outputs a Low logic value in the case wherethe signal S3 a is larger than the signal S3 b. The output 4 a of thiscomparator 430 finctions as a determination signal for the position ofthe rotor 11 in stationary mode.

The foregoing is the description of the generation of the alternatingcurrent between U and V phases and the determination of the rotorposition in FIG. 6. After that, the alternating current is generatedbetween V and W phases and between W and U phases and the rotor positiondetermined similarly.

Specifically, the current amount detector 40 detects the values α and βbetween V and W phases of the load 11 a and controls the alternatingcurrent through the output transistor control circuit 3. The timecounter 41 counts the time t1, t2 between V and W phases of the load 11a, and the time difference amplifier 42 amplifies by converting the load11 a between V and W phases into a voltage signal S3. The rotor positiondeterminator 43, on the other hand, makes the determination of the load11 a between V and W phases in response to the voltage signal S3. Afterthat, the current amount detector 40 detects the values α and β betweenW and U phases of the load 11 a and controls the alternating currentthrough the output transistor control circuit 3. The time counter 41counts the time t1, t2 between W and U phases of the load 11 a, and thetime difference amplifier 42 amplifies by converting the load 11 abetween W and U phases to the voltage signal S3. The rotor positiondeterminator 43 is supplied with the voltage signal S3 and makes thedetermination of the load 11 a between W and U phases.

FIGS. 14, 15 are diagrams for explaining the relation of correspondencebetween the result of generation of the alternating current between thephases and determination of the rotor position on the one hand and theposition of the rotor 10 on the other hand. Take the alternating currentbetween U and V phases as an example. In the case where the time t1during which the alternating current flows in the first direction from Uto V phases is longer than the time t2 during which the alternatingcurrent flows in the second direction from V to U phases, as indicatedby circles 1, 5, 6 in FIG. 14, the difference of voltages of the signalsS3 a, S3 b is negative and the output 4 a of the comparator 430 is Low.

In the process, the relative positions of the rotor 10 and the stator 11can be considered such that they are at any of the positions indicatedby the circles 1, 5, 6 in FIG. 15. Especially, in the case of the circle6 in FIG. 15, the U-phase load of the stator 11 is opposed squarely tothe S pole of the rotor 10 and the V-phase load of the stator 11 issquarely opposed to the N pole of the rotor 10, and therefore thedifference between the inductances L1, L2 becomes most conspicuous.

In the case where the time t1 during which the alternating current flowsin the first direction from U to V phases is shorter than the time t2during which the alternating current flows in the second direction fromV to U phases, on the other hand, as indicated by circles 2, 3, 4 inFIG. 14, the difference of voltages between the signals S3 a, S3 bassumes a positive value, and the output 4 a of the comparator 430 isHi.

In the process, the relative positions of the rotor 10 and the stator 11can be considered such that they are at any of the positions indicatedby the circles 2, 3, 4 in FIG. 15. Especially, in the case of the circle3 in FIG. 15, the U-phase load of the stator 11 is opposed squarely tothe N pole of the rotor 10 and the V-phase load of the stator 11 issquarely opposed to the S pole of the rotor 10, and therefore thedifference between the inductances L1, L2 becomes most conspicuous.

In similar fashion, between V and W phases and between W and U phases,the rotor position is determined by the output 4 a of the comparator430, and therefore, the position of the rotor 10 in stationary mode ismore accurately determined based on the combination of the determinationresults for the respective phases of the load 11 a. Specifically, asshown in FIGS. 14, 15, the rotor position is determined as circle 1 inthe case where the determination result between U and V phases is Low,the determination result between V and W phases is Low and thedetermination result between W and U phases is Hi, as circle 2 in thecase where the determination result between U and V phases is Hi, thedetermination result between V and W phases is Low and the determinationresult between W and U phases is Hi, as circle 3 in the case where thedetermination result between U and V phases is Hi, the determinationresult between V and W phases is Low and the determination resultbetween W and U phases is Low, as circle 4 in the case where thedetermination result between U and V phases is Hi, the determinationresult between V and W phases is Hi and the determination result betweenW and U phases is Low, as circle 5 in the case where the determinationresult between U and V phases is Low, the determination result between Vand W phases is Hi and the determination result between W and U phasesis Low, and as circle 6 in the case where the determination resultbetween U and V phases is Low, the determination result between V and Wphases is Hi and the determination result between W and U phases is Hi.

These determination results indicate the position of the motor rotor instationary mode and is referred to by the output transistor controlcircuit 3 at the time of kick operation.

In the stationary position detection circuit and the motor drive circuitaccording to this embodiment, the time counter 41 counts the time t1,t2, and the time difference amplifier converts the time t1, t2 to thevoltage signal S3 and amplifies the voltage signal S3 in accordance withthe accumulation of the time t1, t2 by the number of alternations of thealternating current. Since the alternating current is used, unlike inthe case where the kickback voltage is used, the voltage signal S3 canbe amplified with an increased number of alternations for a higherdetection accuracy. Also, an increased number of alternations makes itpossible to amplify the voltage signal S3 without increasing the valuesα, β of the alternating current, and therefore, unlike in the case wherethe kickback voltage is used, the alternating current of a large valueis not required to be supplied (about 0.1 A, for example). As a result,the alternating current can be reduced to a small value, and thevibration can be suppressed. In this way, a stationary positiondetection circuit and a motor drive circuit capable of detecting theposition of the rotor 10 more appropriately can be realized.

Also, in the stationary position detection circuit and the motor drivecircuit according to this embodiment, the rotor position determinator 43determines the rotor position based on the voltage signal S3 for eachphase of the load on the one hand and determines the position of therotor 10 in stationary mode also based on the combination of thedetermination results for the respective phases of the load on the otherhand. In view of the fact that the position of the rotor 10 is variedwith the combination of the determination results for the respectivephases of the load, the position of the rotor 10 can be detected moreaccurately.

Further, in the stationary position detection circuit and the motordrive circuit according to this embodiment, the current amount detector40 includes the comparator 401, the AND gate circuit 402 and theD-flip-flop 403 and operates in such a manner that the inversion of theoutput of the D-flip-flop 403 constitutes the detection signal 40 a ofthe values α and β and the control signal 40 a of the alternatingcurrent. Thus, the current amount detector 40 can be configured of asimplified circuit.

Furthermore, in the stationary position detection circuit and the motordrive circuit according to this embodiment, the time counter 41 includesa current source 410 and first and second switches 411, 412, the timedifference amplifier 42 includes first and second capacitors 421, 423,and the rotor position determinator 43 includes a comparator 430. Thus,the time counter 41, the time difference amplifier 42 and the rotorposition determinator 43 can be configured of a simple circuit.

Second Embodiment

This embodiment is a modification of the stationary position detectioncircuit and the motor drive circuit according to the first embodiment,and represents another example of the configuration including the timecounter 41 and the time difference amplifier 42 according to the firstembodiment.

FIG. 16 is a diagram showing a detailed configuration of the timecounter 41 a and the time difference amplifier 42 a in the stationaryposition detection circuit 4 according to this embodiment. The timecounter 41 a includes first and second current sources 410, 413, a firstswitch 411 for selectively outputting the current I1 from the firstcurrent source 410 when the logic value of the detection signal 40 a isLow, and a second switch 412 for selectively drawing the current I1 tothe second current source 413 when the logic value of the detectionsignal 40 a is Hi. The current output from the first switch 411 and thecurrent drawn by the second switch 412 constitute a current signal S4 cwhich is the signal S4.

The time difference amplifier 42 includes a capacitor 424 having apredetermined capacitance with the inter-electrode voltage functioningas a voltage signal S3 a, which is charged by the output of the firstswitch 411 and discharged by the current drawn by the second switch 413,a constant voltage source 426 adapted to provide the initial value ofthe inter-electrode voltage of the capacitor 424 and a switch 425.

One end of the capacitor 424 is connected to the first switch 411 andthe second switch 412, and the other end thereof applied with thegrounding potential GND. The positive terminal of the constant voltagesource 426 is connected to one end of the capacitor 424 through theswitch 425, and the negative terminal thereof applied with the groundingpotential GND. The potential S4 d at the positive terminal of theconstant voltage source 426 represents the signal S3 b making up theother part of the voltage signal S3.

The rotor position determinator 43 includes a comparator 430 havingnegative and positive terminals supplied with the signal S3 aconstituting one part of the voltage signal S3 and the signal S3 bconstituting the other part of the voltage signal S3, respectively, inwhich the output logic value functions as a determination signal 4 a forthe rotor position in stationary mode.

The time counter 41 a shown in FIG. 16 has the function of counting, inaccordance with the detection signal 40 a, the time t1 (the period TB inFIG. 7) for which the alternating current changes from α to β and thetime t2 (the period TC in FIG. 7) for which the alternating currentchanges from β to α, outputting the current signal S4 c for the countedtime t1, and drawing the current signal S4 c for the counted time t2.

Specifically, the first switch 411 in the time counter 41 a, inaccordance with the detection signal 40 a, selectively outputs thecurrent I1 from the first current source 410 during the period (the Lowperiod of the detection signal 40 a) from the detection of the value αto the detection of the value β by the current amount detector 40thereby to count the time t1. On the other hand, the second switch 412in the time counter 41 a, in accordance with the detection signal 40 a,selectively draws the current I1 into the second current source 413during the period (the Hi period of the detection signal 40 a) from thedetection of the value β to the detection of the value α by the currentamount detector 40 thereby to count the time t2.

The time difference amplifier 42 a shown in FIG. 16 converts the signalS4 c constituting the current signal to the voltage signal S3 a, andamplifies the voltage signal S3 a in accordance with the accumulation ofthe time t1, t2 by the number of alternations. Specifically, thecapacitor 424 is applied with an initial value as a voltage generated bythe constant voltage source 426 by temporarily turning on the switch 425through the reset signal S2, after which the switch 425 is turned off.

The capacitor 424 accumulates the charge each time the current signal S4c is input from the first switch 411 turned on during the time t1, andincreases the accumulated charge in accordance with the accumulation ofthe time t1 by the number of alternations thereby to amplify the signalS3 a. The capacitor 424, on the other hand, releases the charge eachtime the current signal S4 c is drawn by the second switch 412 turned onduring the time t2, and decreases the accumulated charge in accordancewith the accumulation of the time t2 by the number of alternationsthereby to reduce the signal S3 a.

Both the current value from the first switch 411 and the current valuedrawn by the second switch 413 are I1. As long as the time t1 and t2have the same value, therefore, the influent current amount and theoutgoing current amount have the same value. Thus, the signal S3 aconstituting inter-electrode voltage of the capacitor 424 remains thesame as the voltage (signal S3 b) generated as an initial value by theconstant voltage source 426. In the case where the time t1 and t2 havedifferent values, however, the signal S3 a, which is amplified by thenumber of times equal to the number of alternations, is output byemphasizing the difference between time t1 and t2, and thereforeconsiderably different from the signal S3 b assuming the initial value.

Incidentally, the reset signal S2 shown in FIG. 16, after thealternating current flows between U and V phases, is activated beforethe alternating current next begins to flow between V and W phases, andsimilarly activated before the alternating current begins to flowbetween W and U phases after flowing between V and W phases. The resetsignal S2 thus prevents the detection result (the charge amount of thecapacitor 424) between the respective phases from affecting the nextdetection between the phases.

The comparator 430 of the rotor position determinator 43 shown in FIG.16 compares the magnitude of the signals S3 a and S3 b, and outputs a Hilogic value in the case where the signal S3 b is larger than the signalS3 a, and a Low logic value in the case where the signal S3 a is largerthan the signal S3 b. The output 4 a of this comparator 430 functions asa determination signal for the position of the rotor 11 in stationarymode.

The operation of the time counter 41 a, the time difference amplifier 42a and the rotor position determinator 43 shown in FIG. 16 is explainedabove. The operation of the other circuits is similar to that of thestationary position detection circuit and the motor drive circuitaccording to the first embodiment and not explained.

In the stationary position detection circuit and the motor drive circuitaccording to this embodiment, the time counter 41 a includes the firstand second current sources 410, 413 and first and second switches 411,412, the time difference amplifier 42 a includes the capacitor 424 andthe constant voltage source 426, and the rotor position determinator 43includes the comparator 430. Thus, the time counter 41 a, the timedifference amplifier 42 a and the rotor position determinator 43 can beconfigured as a simple circuit. Also, the capacitor 424 is the onlycapacitor included in the time difference amplifier 42 a, and thereforethe increase in circuit size can be suppressed.

Third Embodiment

This embodiment is also a modification of the stationary positiondetection circuit and the motor drive circuit according to the firstembodiment, and represents another example of the configuration of thetime counter 41 and the time difference amplifier 42 according to thefirst embodiment.

FIG. 17 is a diagram showing a detailed configuration of a time counter41 b and a time difference amplifier 42 b in the stationary positiondetection circuit 4 according to this embodiment. The time counter 41 bincludes a current source 410, a first switch 411 for selectivelyoutputting the current I1 from the current source 410 when the logicvalue of the detection signal 40 a is Low, a second switch 414 forapplying a predetermined potential when the logic value of the detectionsignal 40 a is Low, a third switch 415 for selectively outputting thecurrent I1 from the current source 410 when the logic value of thedetection signal 40 a is Hi, a fourth switch 412 grounded when the logicvalue of the detection signal 40 a is Hi, and a voltage source 416 forgenerating a predetermined potential. The current output from the firstswitch 411 and the current drawn by the fourth switch 412 constitute acurrent signal S4 f as a signal S4.

The time difference amplifier 42 includes a capacitor 427 of apredetermined capacitance value having a first electrode connected tothe first switch 411 and the fourth switch 412 and a second electrodeconnected to the second switch 414 and the third switch 415, in whichthe voltage between the first and second electrodes finctions as avoltage signal S3 (S3 a, S3 b).

The rotor position determinator 43 includes a comparator 430 and is soconfigured that the second electrode of the capacitor 427 is connectedto the positive input terminal of the comparator 430 and the firstelectrode of the capacitor 427 is connected to the negative inputterminal of the comparator 430. The potential at the first electrode ofthe capacitor 427 constitutes the signal S3 a, and the potential at thesecond electrode of the capacitor 427 constitutes the signal S3 b.

The time counter 41 b shown in FIG. 17, in accordance with the detectionsignal 40 a, counts the time t1 (the period TB in FIG. 7) for which thealternating current changes from α to β and the time t2 (the period TCin FIG. 7) for which the alternating current changes from β to α,outputs the current signal S4 f for the counted time t1, and draws thecurrent signal S4 f for the counted time t2.

Specifically, the first switch 411 and the second switch 414 in the timecounter 41 b, in accordance with the detection signal 40 a, selectivelyoutput the current I1 constituting the current signal S4 f from thecurrent source 410 during the period (the Low period of the detectionsignal 40 a) from the detection of the value α to the detection of thevalue β by the current amount detector 40 thereby to count the time t1.On the other hand, the fourth switch 412 and the third switch 415 in thetime counter 41 b, in accordance with the detection signal 40 a,selectively draw the current I1 to the grounding potential GND throughthe fourth switch 412 as the current signal S4 f during the period (theHi period of the detection signal 40 a) from the detection of the valueβ to the detection of the value α by the current amount detector 40thereby to count the time t2.

The time difference amplifier 42 b shown in FIG. 17 converts the signalS4 f constituting a current signal into voltage signals S3 a, S3 b andamplifies the voltage signals S3 a, S3 b in accordance with theaccumulation of the time t1, t2 by the number of alternations.Specifically, the capacitor 427 accumulates the charge each time thecurrent signal S4 f is input by the turning on of the first switch 411and the second switch 414 during the time t1, and increases theaccumulated charge in accordance with the accumulation of time t1 by thenumber of alternations thereby to amplify the signal S3 a. The capacitor427 releases the charge, on the other hand, each time the current signalS4 f is drawn by the turning on of the fourth switch 412 and the thirdswitch 415 during the time t2, and decreases the accumulated charge inaccordance with the accumulation of time t2 by the number ofalternations thereby to reduce the signal S3 a.

The current value from the first switch 411 is I1, and the current valuedrawn by the fourth switch 412 is also I1. Assuming that the time t1 andt2 have the same value, therefore, the influent current amount and theoutgoing current amount have the same value. Thus, the signals S3 a, S3b constituting inter-electrode voltages of the capacitor 427 develop nopotential difference. In the case where the time t1 and t2 havedifferent values, however, the signals S3 a, S3 b, which are amplifiedby the number of alternations, are output by emphasizing the differencebetween time t1 and t2, and the signals S3 a, S3 b develop a differencein magnitude in accordance with the difference between time t1 and t2.

In order to reset the circuit of FIG. 17 after detection between therespective phases, the first switch 411, the second switch 414, thethird switch 415 and the fourth switch 412 are all turned on. As aresult, the charge accumulated in the capacitor 427 is released.

The comparator 430 of the rotor position determinator 43 shown in FIG.17 compares the signals S3 a and S3 b in magnitude, and in the casewhere the signal S3 b is larger than the signal S3 a, outputs a Hi logicvalue, while in the case where the signal S3 a is larger than the signalS3 b, a Low logic value is output. The output 4 a of this comparator 430finctions as a determination signal for the position of the rotor 11 instationary mode.

The foregoing is the description of the operation of the time counter 41b, the time difference amplifier 42 b and the rotor positiondeterminator 43 shown in FIG. 17. The operation of the other circuits issimilar to that of the stationary position detection circuit and themotor drive circuit according to the first embodiment, and therefore isnot described again.

In the stationary position detection circuit and the motor drive circuitaccording to this embodiment, the time counter 41 b includes a currentsource 410 and first to fourth switches 411, 414, 415, 412, the timedifference amplifier 41 b includes a capacitor 427, and the rotorposition determinator 43 includes a comparator 430. As a result, thetime counter 41 b, the time difference amplifier 42 b and the rotorposition determinator 43 can be configured as a simple circuit. Also,the capacitor 427 is the only capacitor included in the time differenceamplifier 42 b, and therefore the circuit size increase is suppressed.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

1. A motor drive circuit comprising: an output circuit for driving amotor; an output control circuit for controlling said output circuit; aresistor connected to said output circuit; and a detection circuitcoupled to said output circuit for detecting the amount of current insaid resistor and supplying said output control circuit with a controlsignal.
 2. The motor drive circuit according to claim 1, wherein saiddetection circuit includes: a comparator for comparing a voltage at aconnection node between said output circuit and said resistor with apredetermined voltage.
 3. The motor drive circuit according to claim 2,wherein said motor is a three-phase DC brushless motor.
 4. The motordrive circuit according to claim 2, wherein said motor is a Hallsensorless motor.